1. Field of the Invention
The present invention relates in general to a device and method of coating particulates with a liquid. In particular, this invention relates to coating fine granular and particulate hydroscopic matter with a fog of oil and other liquids to reduce powdering and/or to add desirable ingredients to the matter.
2. Description of the Prior Art
Often it is desirable to add small amounts of oil or other liquid to the surface of bulk powders, particulates, or granular material. It is almost always desirable to have uniform coating of the liquid material over all of the surface of the solid material. There are many reasons for coating particulate matter with liquid, among them to reduce dusting which creates waste and is an environmental hazard, to reduce agglomeration of particles that are hydroscopic and tend to bind together into large clumps, and to add chemicals to the particles to achieve some desirable end. This invention is directed towards coating fine and very fine particulates, and in particular particulates of liming material that are hydroscopic and tend to form air borne dust.
There are several methods commonly employed to carry out the coating of particulates with liquids. The first is by adding the liquid to the bulk material in a blender or mixer where, through particle-to-particle contact, the small amount of liquid is distributed to all particles. This technique is not very effective in that the solid particles are porous and absorb the liquid into the particles unevenly. Another problem with this technique in particular is that the mixing or blending is a separate process step and will likely increase the amount of fines in the product which may not be desirable.
A second method of liquid coating particles is to spray the particles with a fine stream or mist of the liquid. If the particles are porous, then the solid material can be sprayed with a fine mist of the liquid in a mixer where the surface of the material that is being sprayed is in constant mixing so as to expose more material to the liquid spray. Finally, the liquid can be added to the solid material and then the material is finely ground so as to coat all of the newly formed powder. This technique would only be effective if a fine ground product was required.
There are several devices that have been designed to spray-coat particulate matter such as seed, wood shavings, or coal. Cooper et al. (U.S. Pat. No. 2,097,914) and Enos (U.S. Pat. No. 4,921,674) were designed to coat coal particles and plant seed, respectively. These devices consist of a hopper with spray devices located inside the hopper, the spray devices being located under fixed baffles that deflected the falling material that is then sprayed. The Barnes et al. (U.S. Pat. No. 4,478,896) invention uses a series of conveyers to transport the solid particles and thus requires many moving parts in its operation. Further, the Barnes et al. device does not afford adequate protection of the spray heads from clogging that can occur with very fine particulates, as the Barnes et al. device is directed towards wood shavings. These devices are relatively complex, requiring many moving parts to operate. Also, these devices may not be well suited for very fine particulates such as in liming dust used for agricultural and construction purposes. Lime and quicklime (CaO and Ca(OH)2) are hydroscopic and thus tend to agglomerate as water is absorbed and reacted. Thus, an improved means of liquid coating these materials is necessary.
Coating particles, especially liming materials, with liquids can have both environmental and economic benefits. Loss of material due to dusting, and its escape into the air (thus creating a pollution hazard) can also be reduced. Due to Environmental Protection Agency (EPA) regulations and other economic reasons, it is highly desirable to make the coating of particles more cost efficient and easier to carry out.
What is needed is an apparatus that can deliver a fog of liquid such as oil that will can coat very fine particles such as liming materials. The present invention is directed towards such a use.
One object of the present invention is to provide an improved means of adding a coat of liquid to fine or very fine particulate matter.
Another object of the invention is to provide a means of applying oil to hydroscopic particulates such as CaO, Ca(OH)2, and other xe2x80x9climingxe2x80x9d materials to prevent the particles from becoming air borne.
Another object of the present invention is to provide a means of creating a fog of liquid mixtures, such as oil and water, that are not miscible.
Another object of the present invention is to provide a means of protecting the liquid fog nozzles of the invention from clogging with the particulate matter.
Yet another object of the present invention is to provide a series of shelves that are adjustable and allow particles to flow by force of gravity.
These objects and others are achieved by application of the device and method of the present invention. The present invention is directed towards a method of agglomeration of fine particles and the addition of desirable chemical compounds to the particles. The method comprises feeding fine particles of solid to an enclosed inclined chute and locating at least a first inclined shelf and a subsequent inclined shelf within the chute, each shelf having an inclined top surface, a bottom surface and a leading edge. An addition funnel fitted with air pads may be used at the top of the chute to facilitate the even and continuous addition of particulates to the chute. Once the particles are fed to the top of the chute, they fall on the top surface of the first inclined shelf and slide down the inclined top surface by force of gravity until falling from the leading edge, thus forming a vertical free flow of particles. At least one liquid fog nozzle is located between the bottom surface of the first shelf and the chute, the fog nozzle creating a fog of liquid in the direction of the leading edge of the first shelf. The fog nozzles create homogeneous droplets of the liquid or liquid mixture through the force of the liquid within the nozzle. Once the particles fall from the shelf, a fog of at least one liquid is applied to the particles as the vertical free flow of particles falls from the leading edge of the first shelf. The inclined positioning of the chute allows gravity to pull the once coated particles to at least a second inclined shelf. After passing over at least the second shelf, the liquid coated particles are discharged through a discharge funnel, the liquid coating preventing excess dusting of the fine particles.
The number of shelves can be varied within the chute. Further, the inclination of the chute relative to the ground and the shelves relative to the chute can be varied. The fog spray nozzles can be independently adjusted, and there can be more than one fog sprayer under each chute for fogging more than one type of liquid on the particles. The chute can also have a discharge funnel for discharging the coated particles into a truck, train car, or other storage or transport means. The discharge funnel can also have a dust collector to recycle uncoated dust particles.
Additional objects, features and advantages will be apparent in the written description which follows.